For example, U.S. Pat. No. 6,186,418 B1 (JP-A-2000-104647) proposes a fuel injection valve having a plate-shaped nozzle device defining therein multiple nozzle holes for injecting fuel being grouped and injected in two directions. In the nozzle device having multiple nozzle holes, atomization of fuel spray is promoted as the diameter of each nozzle hole becomes small. The number of the nozzle holes in the nozzle device need to be increased to maintain predetermined injection quantity when the diameter of the nozzle hole becomes small and the injection quantity from each nozzle hole decreases.
However, since spread angles of sprays and a spread angle of one spray are determined according to each specific performance, the spread angles of the sprays and the spread angle of the one spray itself are constant, even when the number of the nozzle holes increases, As shown in FIG. 16, an imaginary straight line extends in an injection direction along a passage axis of each of nozzle holes 400, 402. That is, the imaginary straight line extends along an extension line each inclined by an angle of inclination of each of the nozzle holes. The imaginary straight lines and an imaginary plane therebetween define intersections 412 on a polygon or a circle. In the present spraying shape, the distance between the intersections 412 adjacent to each other becomes small as the number of the nozzle holes increases in each spray 410 in the two-direction fuel injections. As a result, fuel sprays respectively injected from nozzle holes interfere with each other, and consequently, atomization of the fuel sprays are impaired.
Furthermore, since the intersections 412 are located on the polygon or the circle, an injection quantity of the spray 410 is varied. Specifically, the injection quantity becomes large on the polygon or the circle, on which the intersections 412 are located, and an injection quantity becomes small in the radially inside of the intersection 412. Therefore, deviation in distribution of the injection quantity becomes large in the spray 410.
In addition, as shown in FIG. 17, the imaginary straight lines, each of which extends in the injection direction along the passage axis of each of nozzle holes 420, 422, and an imaginary plane therebetween define intersections 432 on a polygon, which is inwardly dented. Even in the present spraying shape, the distance between the intersections 432 adjacent to each other becomes small as the number of the nozzle holes increases in each spray 430 in the two-direction fuel injections. Consequently, atomization of the fuel sprays is impaired, and deviation in distribution of the injection quantity becomes large.
When atomization of the fuel spray is impaired and deviation in distribution of injection quantity becomes large, mixture of fuel and the air becomes insufficient and hence, unburnt components such as HC increase in the exhaust gas.